Modify > Copy/Delete > Warning settings can be a lifesaver if something happens with the disk structure, in special if one uses mirror for backup.

However, there's a catch: lowest value possible is 1%.
Unfortunately, for today's big disks, 1% may be too much:
- 1% of 2 TB is 20 GB;
- 1% of 4 TB is 40 GB and so on.

Would ask warning settings to allow either lower percentages or explicit amounts in MB.
That would make it really safer to backup.

Personal history:
I have been using SyncBackPro for years and days ago realized that a 2 TB disk that used to be almost full was almost empty.
Looked at the folder structure, it seemed OK.
Recycle Bin, empty.
Looking further I noted that folders were there, but files had gone.
My backup (mirrored) showed the same situation.
What probably happened was that SyncBackPro duly mirrored a corrupted volume during one of my weekly backup sessions and I was unaware.
Until days ago, I had not a warning set...

Fortunately I have been able to rescue almost all files (2 TB!) with Recuva, a 20 hour plus operation; but a number of files could not be rescued.